I have a new .net WebApi project that I’m trying to get set up with Entity Core.
I did my initial migrations and it successfully created a Migration class in the Migrations Folder.
I tried to then update the database:
dotnet ef database update

and it fails with:

PS C:UsersdavidDocumentsProgrammingProjectsdotnetShopBacksrcShopBack> dotnet ef database update
Build started...
Build succeeded.
System.ArgumentException: Host can't be null
   at Npgsql.NpgsqlConnectionStringBuilder.PostProcessAndValidate()
   at Npgsql.NpgsqlConnection.SetupDataSource()
   at Npgsql.NpgsqlConnection.set_ConnectionString(String value)
   at Npgsql.NpgsqlConnection..ctor(String connectionString)
   at Npgsql.NpgsqlConnection.CloneWith(String connectionString)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlRelationalConnection.CloneWith(String connectionString)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlDatabaseCreator.Exists(Boolean async, CancellationToken cancellationToken) 
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlDatabaseCreator.Exists()
   at Microsoft.EntityFrameworkCore.Migrations.HistoryRepository.Exists()
   at Microsoft.EntityFrameworkCore.Migrations.HistoryRepository.GetAppliedMigrations()
   at Npgsql.EntityFrameworkCore.PostgreSQL.Migrations.Internal.NpgsqlMigrator.Migrate(String targetMigration)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.UpdateDatabase(String targetMigration, String connectionString, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabaseImpl(String targetMigration, String connectionString, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabase.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Host can't be null

I have found a few posts from years ago with this issue but none of them had a solution.

Program.cs

using Microsoft.EntityFrameworkCore;
    using ShopBack.Services;
    
 
    var builder = WebApplication.CreateBuilder(args);
    {
       
        builder.Services
        .AddScoped<ProductsService>()  
        .AddControllers(options => options.SuppressAsyncSuffixInActionNames = false);
        
        builder.Services.AddDbContext<LibraryContext>(options =>
        {
            options.UseNpgsql(builder.Configuration.GetConnectionString("YourConnectionName"));
        });
        
    }
    
    var app = builder.Build();
    {
        //configure request pipeline
        app.MapControllers();
    
        app.UseCors (x => x
            .AllowAnyOrigin()
            .AllowAnyMethod()
            .AllowAnyHeader());
    }
    
    app.Run();

appsettings.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "YourConnectionName": "Host=127.0.0.1; Port=5432; User Id=postgres; Password=postgres; Database=shopback"
  }
}

appsettings.Development.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "YourConnectionName": "Host=127.0.0.1; Port=5432; User Id=postgres; Password=postgres; Database=shopback"
  }
}

.cjsproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="8.0.7">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>

    <PackageReference Include="Npgsql" Version="8.0.3" />

    <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="8.0.4" />

  </ItemGroup>

  <ItemGroup>
    <None Update="appsettings.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>

</Project>